Re: [PATCH] TCP Zero Copy for mmapped files

[David S. Miller]

   From: Alan Cox <[e-mail]>
   Date: 02 Jan 2003 23:20:44 +0000

   On Thu, 2003-01-02 at 22:28, Larry McVoy wrote:
   > The VM cost hurts.  Badly.  Imagine that the network costs ZERO.  Then
   > the map/unmap/vm ops become the dominating term.  That's why it is a
   > fruitless approach, it still has a practical limit which is too low.
   
   It depends how predictable your content is. With a 64bit box and a porn
   server its probably quite tidy
   
Let's say you have infinite VM (which is what 64-bit almost is :) then
the cost is setting up all of these useless VMAs for each and every
file (which is a 1 time cost, ok), and also the VMA lookup each
write() call.

With sendfile() all of this goes straight to the page cache directly
without a VMA lookup.